Rock Mass Characterisation Using Drill Performance Monitoring : Problems, Analysis challenges and Limitations

In open pit mining, it is important to know as much information as possible about rock masses to be mined for more cost-effective mining operation. In rock engineering perspective, information about rock mass characteristics usually includes hardness of the rock, geological features, fractures, faults, ore contacts, water bearing stratum. The information about large scale rock mass characterisation is still based on traditional methods such as widely spacedcore drillings, geological mapping of exposed walls, analysis of drill cutting, etc but these methods involve uncertainty about rock mass characteristics in uncored areas. In addition, they are expensive and time consuming. The need for more inexpensive methods providing high resolution rock mass characterisation over large mining areas is therefore a priority forfuture mining industry. Measurement While Drilling (MWD) is a well-established drill monitoring technique which provides information about the rock mass in each production hole. This technique is inexpensive and also ensures high resolution information. By using this technique, drill parameters such as penetration rate, feed force, rotation speed, rotation torque and air pressure are recorded during production drilling which can be used to characterise the penetrated rock mass. However, recorded parameters are not only influencedby the variation of rock mass characteristics; they are also affected by the operators, rig control system interventions, bit wear and measurement errors. In order to use this large amount of data on recorded parameters for the purpose of rock mass characterisation, it is necessary to improve our existing understanding about the contribution of all the influencingfactors and to develop the techniques for identifying and minimising the effect of those factors on rock mass characterisation. The focus of this thesis is to evaluate Measurement While Drilling (MWD) system as a tool for large scale rock mass characterisation in rotary blast hole drilling. In this thesis, researchmethods mainly include literature review, data collection, processing, integration, and analysis. The data have been collected from one of the operating open pit mines in Sweden. Multivariate analysis has been performed to assess the wear of the bit. This thesis presents an attempt to evaluate recorded penetration rate and calculated specific energy for rock mass characterisation. Penetration rate is considered as resistance to crushingof the rock while the calculated specific energy is taken as an index of the mechanical efficiency of a rock working process. The analysis shows that horizontal maps of penetration rate and specific energy (hole average) value reflects the variation of rock mass characteristics in a bench. The areas in the bench which have comparatively higher penetration rate and lower specific energy reflect possible interaction between the bit and soft or weak rock orheavily jointed rock. In contrast some areas in the bench have a relatively lower penetration rate and higher specific energy, indicating possible interaction between the bit and hard rock. In addition, using penetration rate and specific energy values between two subsequent benches indicate similar boundaries among the penetrated zones. When plotting specific energy against penetration rate in each bench, a clear inverse non-linear relationship has beenfound between those parameters. This correlation indicates that penetration rate and specific energy can indicate rock mass behaviour. Further, statistical analysis is done to observe the statistical significance of penetration rate and specific energy values among the different penetrated areas in the bench. The results indicate that penetration rate and specific energy can be used for characterizing large scale rock masses. In addition, information about the rockmass in the upper bench can possibly be used in the next bench to improve production planning. However, hole by hole analysis shows penetration rate and specific energy are influenced by bit wear, hole depth variables, flushing system, operator influence, drill control system, etc.Principal Component Analysis (PCA) shows that penetration rate and specific energy reflecting the change of rock mass characteristics basically are not correlated to bit life length. The bit life length seems instead to be well correlated to the operational parameters such as rotation torque, rotation speed and to a minor extent feed force. Conclusions from PCA analysis must be conservative since the explanation rate for the first two components islimited to 56.5%. Further, the analysis shows that recorded penetration rate has a negative trend with the increasing hole depth. The calculated specific energy has a positive trend with the increasing hole depth. This means that recorded parameters are influenced by hole depth variables.The flushing system also influences recorded parameters. The analysis shows that constant air pressure from the collaring point to the end does not give a clear indication of better flushing system as frequent joints and regular water ingression usually cause fluctuation of pressure.Some of the above mentioned problems can be handled to minimise the effect of influencing factors on recorded parameters. The direct effect of bit wear and hole depth dependency can be minimised by generating a horizontal map of recorded data (e.g. penetration rate) over a large area in the bench. Hole depth dependency on recorded parameters can also be neutralised by performing normalisation based on a regression line using simple geometry. Inshort, the effect of influencing factors on the recorded parameters obtained by using the Measurement While Drilling technique can be minimised and, this technique, in turn, can become a useful tool for large scale rock mass characterisation.Godkänd; 2015; 20150423 (rajgho); Nedanstående person kommer att hålla licentiatseminarium för avläggande av teknologie licentiatexamen. Namn: Rajib Ghosh Ämne: Drift och underhållsteknik/Operation and Maintenance Engineering Uppsats: Rock Mass Characterisation Using Drill Performance Monitoring Examinator: Håkan Schunnesson Institutionen för samhällsbyggnad och naturresurser Avdelning Geoteknologi Luleå tekniska universitet Diskutant: Professor Piyush Rai Indian Institute of Technology (BHU) Varanasi, Indien Tid: Tisdag 9 juni 2015 kl 10.00 Plats: F1031, Luleå tekniska universite